Crown ether containing pem electrode

ABSTRACT

A membrane electrode assembly for fuel cells includes a proton conducting membrane having a first side and a second side. The membrane electrode assembly further includes an anode disposed over the first side of the proton conducting layer and a cathode catalyst layer disposed over the second side of the proton conducting layer. One or both of the anode catalyst layer and the cathode catalyst layer includes a first polymer which has cyclic polyether groups. An ink composition for forming a fuel cell catalyst layer is also provided.

FIELD OF THE INVENTION

In at least one aspect, the present invention relates to proton exchangemembranes and electrodes for fuel cells with improved stability.

BACKGROUND

Fuel cells are used as an electrical power source in many applications.In particular, fuel cells are proposed for use in automobiles to replaceinternal combustion engines. A commonly used fuel cell design uses asolid polymer electrolyte (“SPE”) membrane or proton exchange membrane(“PEM”) to provide ion transport between the anode and cathode.

In proton exchange membrane type fuel cells, hydrogen is supplied to theanode as fuel and oxygen is supplied to the cathode as the oxidant. Theoxygen can either be in pure form (O₂) or air (a mixture of O₂ and N₂).PEM fuel cells typically have a membrane electrode assembly (“MEA”) inwhich a solid polymer membrane has an anode catalyst on one face, and acathode catalyst on the opposite face. The anode and cathode layers of atypical PEM fuel cell are formed of porous conductive materials, such aswoven graphite, graphitized sheets, or carbon paper to enable the fueland oxidant to disperse over the surface of the membrane facing thefuel- and oxidant-supply electrodes, respectively. Each electrode hasfinely divided catalyst particles (for example, platinum particles)supported on carbon particles to promote oxidation of hydrogen at theanode and reduction of oxygen at the cathode. Protons flow from theanode through the ionically conductive polymer membrane to the cathodewhere they combine with oxygen to form water which is discharged fromthe cell. The MEA is sandwiched between a pair of porous gas diffusionlayers (“GDL”) which, in turn, are sandwiched between a pair ofnon-porous, electrically conductive elements or plates. The platesfunction as current collectors for the anode and the cathode, andcontain appropriate channels and openings formed therein fordistributing the fuel cell's gaseous reactants over the surface ofrespective anode and cathode catalysts. In order to produce electricityefficiently, the polymer electrolyte membrane of a PEM fuel cell must bethin, chemically stable, proton transmissive, non-electricallyconductive and gas impermeable. In typical applications, fuel cells areprovided in arrays of many individual fuel cells arranged in stacks inorder to provide high levels of electrical power. Although the catalystlayers used in fuel cells work reasonably well, there is a need forimproved fuel cell catalyst layers.

Accordingly, there is a need for catalyst layers with improved chemicalstability.

SUMMARY OF THE INVENTION

The present invention solves one or more problems of the prior art byproviding a membrane electrode assembly for a fuel cell. The membraneelectrode assembly includes a proton conducting membrane having a firstside and a second side. The membrane electrode assembly further includesan anode disposed over the first side of the proton conducting layer anda cathode catalyst layer disposed over the second side of the protonconducting layer. At least one of the anode catalyst layer and thecathode catalyst layer includes a first polymer having an ionophore.Characteristically, the ionophore is a cyclic polyether group.

In another embodiment, an ink for forming fuel cell catalyst layers isprovided. The ink composition includes a first polymer including cyclicpolyether groups, a catalyst composition; and a solvent system.

In yet another embodiment, a fuel cell incorporating the membraneelectrode assemblies set forth above is provided. The fuel cell includesa membrane electrode assembly interposed between an anode gas diffusionlayer and a cathode gas diffusion layer. The resulting assembly istypically interposed between an anode flow field plate and a cathodeflow field plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will become more fullyunderstood from the detailed description and the accompanying drawings,wherein:

FIG. 1 is a schematic illustration of a fuel cell that incorporates aPEM with a polymer including cyclic polyether groups;

FIG. 2 provides a synthetic pathway for cyclic polyether compounds withthe following: (i) ClH₂CCOOH/K⁺⁻OBu-t; (ii) CH₃OH/H⁺; (iii) NaOH; (iv)oxalyl chloride or a. NaOH, b. pyridine/SOCl₂; (v)1,4,10,13-tetraoxa-7,16-diazacyclooctadecane; (vi) LiAlH₄ or BH₃/THF;(vii) H⁺; (viii) methyltriphenylphosphonium bromide/n-butyllithium; (ix)methylmagnesium iodide; (x) p-toluenesulfonic acid;

FIG. 3 provides a synthetic pathway for cyclic polyether compounds withthe following: Pathway 6. (i) ClH₂CCOOH/K⁺⁻Ot-Bu; (ii) CH₃OH/H⁺; (iii)NaOH; (iv) oxalyl chloride or a. NaOH, b. pyridine/SOCl₂; (v)1,4,10,13-trioxa-7,13-diazacyclopentadecane; (vi) LiAlH₄ or BH₃/THF;(vii) H⁺; (viii) methyltriphenylphosphonium bromide/n-butyllithium; (ix)methylmagnesium iodide; (x) p-toluenesulfonic acid;

FIG. 4 provides components used in the preparation of cyclic polyethers(including isomers, such as meta- and para-);

FIG. 5 provides components and reactions used in the preparation ofcyclic polyethers (including isomers, such as meta- and para-);

FIG. 6 provides components and reactions used in the preparation ofcyclic polyethers (including isomers, such as meta- and para-);

FIG. 7 provides a synthetic pathway for cyclic polyether compounds withthe following: (i) Br₂/Fe/CH₂Cl₂; (ii) n-butyllithium/THF, −30° C.;(iii) bipyridine; (iv) dimethoxymethane, acetyl chloride, methanol, andSnCl₄ in CH₂Cl₂; (v) ortho-phenanthroline-4-amine; (vi) 1-aza-15-crown-5in THF; (vii) 2-hydroxymethyl-15-crown-5 in THF with NaH; (viii)2-hydroxymethyl[2.2.1]cryptand in THF with NaH, (ix) 1-aza-18-crown-6 inTHF; (x) 2-hydroxymethyl-18-crown-6 in THF with NaH; (xi)2-hydroxymethyl[2.2.2]cryptand in THF with NaH (It should be noted thatthe lower-ring structure analogs are also possible via this scheme);

FIG. 8 provides a synthetic pathway for cyclic polyether compounds withthe following: (i) TiCl₃*AA/diethylaluminum chloride in toluene; (ii)2-hydroxymethyl-18-crown-6 in THF with NaH; (iii)2-hydroxymethyl[2.2.2]cryptand (It should be noted that the lower-ringstructure analogs are also possible via this scheme);

FIGS. 9A and 9B provide scanning electron microscope (SEM) images of amembrane electrode assembly at beginning of life and after 30,000current-voltage (C-V) cycles of a baseline cathode without a cycliccrown additive;

FIGS. 10A and 10B provide SEM images of a membrane electrode assemblywith 5 wt % poly(vinylbenzo-18-crown-6) additive in the cathode atbeginning of life and after 30,000 C-V cycles;

FIGS. 11A and 11B provide 50-cm² active area fuel cell performance of amembrane electrode assembly with 5 wt. % poly(vinylbenzo-18-crown-6)additive in the cathode (A) and a catalyst mass activity plot atbeginning of life (B);

FIGS. 12A and 12B provide 50-cm² active area fuel cell performance of amembrane electrode assembly with 5 wt. % poly(vinylbenzo-18-crown-6)additive in the cathode (A) and a catalyst mass activity plot after10,000 C-V cycles (B);

FIGS. 13A and 13B provide 50-cm² active area fuel cell performance of amembrane electrode assembly with 5 wt. % poly(vinylbenzo-18-crown-6)additive in the cathode (A) and a catalyst mass activity plot after30,000 C-V cycles (B);

FIGS. 14A and 14B provide 50-cm² active area fuel cell performance of abaseline membrane electrode assembly without cyclic crown ether additivein the cathode (A) and a catalyst mass activity plot at beginning oflife (B);

FIGS. 15A and 15B provides 50-cm² active area fuel cell performance of abaseline membrane electrode assembly without cyclic crown ether additivein the cathode (A) and a catalyst mass activity plot after 10,000 C-Vcycles (B); and

FIGS. 16A and 16B provide 50-cm² active area fuel cell performance of abaseline membrane electrode assembly without cyclic crown ether additivein the cathode (A) and a catalyst mass activity plot after 30,000 C-Vcycles (B).

DESCRIPTION OF THE INVENTION

Reference will now be made in detail to presently preferredcompositions, embodiments and methods of the present invention, whichconstitute the best modes of practicing the invention presently known tothe inventors. The Figures are not necessarily to scale. However, it isto be understood that the disclosed embodiments are merely exemplary ofthe invention that may be embodied in various and alternative forms.Therefore, specific details disclosed herein are not to be interpretedas limiting, but merely as a representative basis for any aspect of theinvention and/or as a representative basis for teaching one skilled inthe art to variously employ the present invention.

Except in the examples, or where otherwise expressly indicated, allnumerical quantities in this description indicating amounts of materialor conditions of reaction and/or use are to be understood as modified bythe word “about” in describing the broadest scope of the invention.Practice within the numerical limits stated is generally preferred.Also, unless expressly stated to the contrary: percent, “parts of,” andratio values are by weight; the term “polymer” includes “oligomer,”“copolymer,” “terpolymer,” and the like; the description of a group orclass of materials as suitable or preferred for a given purpose inconnection with the invention implies that mixtures of any two or moreof the members of the group or class are equally suitable or preferred;molecular weights provided for any polymers refers to number averagemolecular weight; description of constituents in chemical terms refersto the constituents at the time of addition to any combination specifiedin the description, and does not necessarily preclude chemicalinteractions among the constituents of a mixture once mixed; the firstdefinition of an acronym or other abbreviation applies to all subsequentuses herein of the same abbreviation and applies mutatis mutandis tonormal grammatical variations of the initially defined abbreviation;and, unless expressly stated to the contrary, measurement of a propertyis determined by the same technique as previously or later referencedfor the same property.

It is also to be understood that this invention is not limited to thespecific embodiments and methods described below, as specific componentsand/or conditions may, of course, vary. Furthermore, the terminologyused herein is used only for the purpose of describing particularembodiments of the present invention and is not intended to be limitingin any way.

It must also be noted that, as used in the specification and theappended claims, the singular form “a,” “an,” and “the” comprise pluralreferents unless the context clearly indicates otherwise. For example,reference to a component in the singular is intended to comprise aplurality of components.

Throughout this application, where publications are referenced, thedisclosures of these publications in their entireties are herebyincorporated by reference into this application to more fully describethe state of the art to which this invention pertains.

With reference to FIG. 1, a fuel cell having a membrane electrodeassembly that incorporates cyclic polyether moieties is provided. Fuelcell 10 includes the membrane electrode assembly 12 which includes anodecatalyst layer 14, cathode catalyst layer 16, and ion conductingmembrane (i.e., proton exchange membrane) 20. Proton (i.e., ion)conducting membrane 20 is interposed between anode catalyst layer 14 andcathode catalyst layer 16 with anode catalyst layer 14 disposed over thefirst side of proton conducting membrane 20 and cathode catalyst layer16 disposed over the first side of proton conducting membrane 20.Characteristically, one or both of anode catalyst layer 14 and cathodecatalyst layer 16 includes a first polymer having cyclic polyethergroups. In a variation, fuel cell 10 also includes porous gas diffusionlayers 22 and 24. Gas diffusion layer 22 is disposed over anode catalystlayer 14 while gas diffusion layer 24 is disposed over cathode catalystlayer 16. In yet another variation, fuel cell 10 includes anode flowfield plate 26 disposed over gas diffusion layer 22 and cathode flowfield plate 28 disposed over gas diffusion layer 24.

The present embodiment includes a first polymer having cyclic polyethergroups. In a refinement, the first polymer having cyclic polyethergroups is part of a polymeric bead. In a refinement, the cyclicpolyether groups are monocyclic or polycyclic (e.g., 2 rings) having 12to 45 member rings. In another refinement, the cyclic polyether groupsare monocyclic or polycyclic (e.g., 2 rings) having 12 to 42 memberrings. In another refinement, the cyclic polyether groups are monocyclicor polycyclic (e.g, 2 rings) having 12 to 39 member rings. In stillanother refinement, the cyclic polyether groups are monocyclic orpolycyclic (e.g, 2 rings) having 12 to 36 member rings. In a refinement,the size of each ring in the cyclic polyether groups is a multiple ofthree. Examples of suitable polymers having cyclic polyether groupsinclude polymers or polymeric beads including crown ether or cryptandgroups. In a further refinement, one or more atoms in the polyether ringmay be substituted by nitrogen atoms (azacrowns) or sulfur atoms(thiacrowns). The crown ether may also be substituted at any locationalong its polyether ring by any of a variety of groups known to thoseskilled in the art.

In the context of the present invention, the polymers having cyclicpolyether groups are ionophores. Such ionophores work advantageously inthree different ways. First, ionophores when added to ionomer solutionssequester metals ions which are initially present as impurities in theionomers and the solvents. Some of the sequestered metal ions includethe Fenton's active catalysts that form hydroxyl radical with hydrogenperoxide such as iron(II), nickel(II), cobalt(II) and copper ions. Othercations, such as aluminum(III), sodium, potassium, and the like, arealso sequestered. As complexes with ionophores, these ions do not asreadily form hydroxyl radicals by reaction with hydrogen peroxide in themembranes like the free ions such as Fe²⁺. Hydrogen peroxide isgenerated as a side reaction by the electrode catalyst during fuel celloperation, and hydroxyl radicals are known to cause chemical degradationfailures in fuel cell membranes. In this way, the ionophores act as achemical mitigant to prevent membrane degradation. Second, theseionophores act to sequester metal ions that are introduced into themembranes as contaminants during fuel cell operation, and in particular,Fe²⁺ generated from the reaction of acidic fuel cell by-products (suchas HF) with stainless steel plates. The metal ionophore complexesprevent a parasitic, autocatalytic degradation due to Fe²⁺ introducedduring fuel cell operation. Third, the ionophores with sequestered metalions can be removed entirely from the ionomer coating solutions bycentrifugation before the membrane is coated. The metal ions bind to theionophores forming a complex which are removed by centrifugation. Inthis way, treatment of ionomer solutions can be used to purify ionomersolutions before electrode layer coating takes place. This separationprocess is especially advantageous when the ionophore-metal complexesare in the form of insoluble beads, fibers, particles precipitates, orsediments. All three mechanisms involving polymeric metal ionophorecomplexes are beneficial in improving the chemical stability of fuelcell membranes. In the electrode, the cyclic crown ether polymerssequester platinum and prevent its migration in the electrode layer tothe membrane. In this way, the cyclic ethers stabilize the cathode layerand enhance durability and electrode life.

As set forth above, membrane electrode assembly 12 includes an anodecatalyst layer 14 and cathode catalyst layer 16 which include a polymerhaving cyclic polyether groups. Polymeric ionophores such as polymershaving cyclic polyether groups are added to Pt on carbon with ionomersolutions before casting polyelectrolyte electrodes (i.e., catalystlayers) for fuel cells. In a variation, the catalyst layers are formedby depositing a catalyst ink on ion conducting membrane 20 by directspraying or coating in a shim frame. In still another variation, thecatalyst layers are formed on a decal and transferred to ion conductingmembrane 20. Alternatively, a catalyst/ionomer ink can be coated on agas diffusion medium substrate, which is known as a catalyst coateddiffusion media (CCDM). The catalyst inks are typically prepared as asolution of a first polymer having polymers having cyclic polyethergroups and second polymer which is a proton conducting polymer orionomer (e.g. NAFION®), with particles of electrically conductivematerial, typically carbon, and particles of catalyst. The electricallyconductive material, e.g., carbon, is typically the catalyst support ofthe ink and the catalyst is typically a metal. In a variation, thecatalyst layer dispersion consists of a mixture of the precious metalcatalyst supported on high surface carbon (e.g., Vulcan XC-72) the firstpolymer having polymers having cyclic polyether groups, and the secondpolymer (an ionomer solution such as NAFION® (DuPont Fluoroproducts,NC)) in a solvent. Examples of useful catalysts include, but are notlimited to, metals such as platinum, palladium; and mixtures of metalsplatinum and molybdenum, platinum and cobalt, platinum and ruthenium,platinum and nickel, and platinum and tin. The second polymer istypically purchased as an ionomer in a solvent and at the desiredinitial concentration. Additional solvent is optionally added to adjustthe ionomer concentration to a desired concentration. In a refinement,the catalyst inks optionally contain polytetrafluoroethylene. Thecatalyst and catalyst support are dispersed in the ink by techniquessuch as ultrasonication or ball-milling. Typically, the averageagglomerate size is in the range from 50 to 500 nm.

In a refinement, the ink composition includes a catalyst composition inan amount of about 1 weight percent to 10 weight percent of the totalweight of the catalyst composition. Characteristically, the catalystcomposition includes catalytically active material on carbon (e.g.,platinum on carbon) dispersed within an ionomer solution with a solvent.The amount of catalytically active material is present in an amount fromabout 5 weight percent to about 40 weight percent of the catalystcomposition. In a refinement, the ink composition includes ionomers inan amount from about 5 weight percent to about 40 weight percent of thecatalyst composition. In another refinement, the ink compositionincludes polymers having cyclic ether groups in an amount from about0.005 weight percent to about 10 weight percent of the catalystcomposition. In a particular refinement, the solvent makes up about 20to 89.095 weight percent of the total weight of the ink composition.Useful solvents include, but are not limited to, alcohols (e.g.,propanol, ethanol, methanol), water, or a mixture of water and alcohols.Characteristically, the solvents evaporate at room temperature.

In another variation, the catalyst inks are homogenized by ball-millingfor about three days before coating on the PEM, decal substrate, or gasdiffusion medium. For shim coating, the catalyst loading can becontrolled by the thickness of the shim; for the Mayer wire-wound rodcoating, the catalyst loading can be controlled by the wire number.Multiple coatings can be applied for higher catalyst loading, as needed.After applying the wet ink, the solvents are dried in an oven to driveoff the solvent and form the electrode. After the catalyst/ionomercoated decal dries, the catalyst/ionomer is then transferred onto a PEMby hot press to form a MEA. The anode and cathode can be hot-pressedonto a PEM simultaneously.

Examples of cyclic polyether groups used in the embodiments andvariation set forth above include, but are not limited to, the followingstructures:

As used herein, the line crossed by a wiggly line in the chemicalformulae represents the point of attachment of a chemical group to apolymer or other chemical group or structure.

In a variation of the present embodiment, the first polymer havingcyclic polyether groups is a polymer. As used herein, the term polymerincludes oligomers. In a refinement, such a polymer is a linear polymer.Such a linear polymer may be represented by the following formulae:

where R₁ is absent or a hydrocarbon group and CPG is a cyclic polyethergroup. When R₁ is absent the polymer with formula (25) reduces to:

In a refinement, the CPG is selected from the groups of formulae 1through 24. Examples of hydrocarbon groups for R₁ include but are notlimited to, C₁₋₂₀ alkyl groups, C₁₋₁₈ polyether groups, C₆₋₂₀ alkylarylgroups, C₆₋₂₀ aryl groups (e.g., phenyl, naphthyl, etc), C₁₋₁₀ alkylgroups, or C₁₋₅ alkyl groups. As used herein, alkylaryl groups aregroups in which an alkyl group is attached to an aromatic group (e.g.,phenyl). In such groups, the alkyl group is bonded to the polymericbackbone and the aromatic group to the cyclic polyether group or thearomatic group is bonded to the polymeric backbone and the alkyl groupis bonded to the cyclic polyether group. It should be appreciated thatthese examples include substituted or unsubstituted alkyl groups as wellas branched or unbranched groups. Examples of substituted groups haveone or more hydrogen atoms replaced by Cl, F, Br, OH, NO₂, —CN, and thelike. In a refinement, the polymers having formulae (24) and (25) areformed by polymerization of compounds having formula (26) and (27)respectively:

In a refinement, the first polymer having cyclic polyether groups ispresent in an amount from about 0.01 to about 10 weight percent of thetotal weight of the anode catalyst layer or the cathode catalyst layer.In another refinement, the first polymer having cyclic polyether groupsis present in an amount from about 0.01 to about 5 weight percent of thetotal weight of the anode catalyst layer or the cathode catalyst layer.In still another refinement, the first polymer having cyclic polyethergroups is present in an amount from about 0.02 to about 3 weight percentof the total weight of the anode catalyst layer or the cathode catalystlayer.

In another variation, the first polymer including cyclic polyethergroups is a cyclic oligomer. Such cyclic oligomers may be formed frompolymerization (e.g., emulsion polymerization) of compounds havingformula 26 or 27 and a divinyl compound such as a compound described byformula 28:

═—R₂—═

where R₂ is a hydrocarbon group. Examples of suitable hydrocarbon groupsfor R₂ include, but are not limited to, C₁₋₂₀ alkyl groups, C₆₋₂₀dialkylaryl groups, C₆₋₂₀ aryl groups (e.g., phenyl, naphthyl, etc),C₁₋₁₀ alkyl groups, or C₁₋₅ alkyl groups. A dialkylaryl group includesan aromatic ring with two alkyl groups bonded thereto. An example ofsuch a cyclic oligomer has the following formula formulae (29A and 29B):

In a variation, the cyclic oligomer is formed by polymerization (e.g.,emulsion polymerization) of a compound having formula 34 or 35, in thepresence of a compound with the general formula 28. Compound 30 anddivinylbenzene are examples of compounds having the generic formula 28.

where n and m are each independently an integer from 1 to 8. In arefinement, n and m are each independently an integer from 1 to 4. In afurther refinement, n and m are equal. Such polymerization may or maynot be in the presence of a compound having formula 28.

As set forth above, membrane electrode assembly 12 includes a secondpolymer having sulfonic acid groups. Examples of such ion conductingpolymers include, but are not limited to, perfluorosulfonic acid (PFSA)polymers, polymers having perfluorocyclobutyl (PFCB) moieties, andcombinations thereof. Examples of useful PFSA polymers include acopolymer containing a polymerization unit based on a perfluorovinylcompound represented by:

CF₂═CF—(OCF₂CFX¹)_(m)—O_(r)—(CF₂)_(q)—SO₃H

where m represents an integer of from 0 to 3, q represents an integer offrom 1 to 12, r represents 0 or 1, and X¹ represents a fluorine atom ora trifluoromethyl group and a polymerization unit based ontetrafluoroethylene. Suitable polymers including perfluorocyclobutylmoieties are disclosed in U.S. Pat. Pub. No. 2007/0099054, U.S. Pat. No.7,897,691 issued Mar. 1, 2011; U.S. Pat. No. 7,897,692 issued Mar. 1,2011; U.S. Pat. No. 7,888,433 issued Feb. 15, 2011, U.S. Pat. No.7,897,693 issued Mar. 1, 2011; and U.S. Pat. No. 8,053,530 issued Nov.8, 2011, the entire disclosures of which are hereby incorporated byreference. Examples of perfluorocyclobutyl moieties are:

The following examples illustrate the various embodiments of the presentinvention. Those skilled in the art will recognize many variations thatare within the spirit of the present invention and scope of the claims.

Synthetic Overview of Polymer-Bound Crown Ethers and Cryptands

The preparations of 2-hydroxymethyl-18 -crown-6 (compound 31),2-hydroxymethyl-15-crown-5 (compound 32), and2-hydroxymethyl-[2.2.2]cryptand (compound 33) are described in FernandoMontanari and Pietro Tundo, “Hydroxymethyl Derivatives of 18-Crown-6 and[2.2.2]Cryptand: Versatile Intermediates for the Synthesis of Lipophilicand Polymer-Bonded Macrocyclic Ligands,” J. Org. Chem., 1982, 47,1298-1302; the entire disclosure of which is hereby incorporated byreference:

Alcohols are easily converted to compounds with vinyl groups, forexample by reaction with 1-(chloromethyl)-3-vinylbenzene or1-(chloromethyl)-4-vinylbenzene. An alternative synthesis routes to2-hydroxymethyl-18-crown-6, 2-hydroxymethyl-15-crown-5, and2-hydroxymethyl-[2.2.2]cryptand are reported in a Ph. D. dissertation byDavid Alan Babb, “Synthesis and Metal Ion Complexation of SyntheticIonophores,” A Ph.D. Dissertation in Chemistry, Texas Tech University,December, 1985; the entire disclosure of which is hereby incorporated byreference.

The syntheses of 4′-vinylbenzo-crown ethers such as compounds 34 and 35are reported in J. Smid, B. El Haj, T. Majewicz, A. Nonni, and R. Sinta,“Synthesis of 4′-vinylbenzocrown ethers.” Organic Preparations andProcedures Int., 1976, 8(4), 193-196.

It should be noted that a bisvinylbenzo-macrocyle is also made in onestep by the reaction of compound 36 with methyltriphenylphosphoniumbromide and n-butyllithium in diethyl ether or tetrahydrofuran (theWittig reaction).

Another approach to compounds 34 and 35 is reported in the reference: S.Kopolow, T. E. Hogen Esch, and J. Smid, “Poly(vinylmacrocyclicpolyethers). Synthesis and Cation Binding Properties,” Macromolecules,1973, 6, 133; the entire disclosure of which is hereby incorporated byreference.

4′-Vinylbenzo[2.2.2]cryptand and 4′-vinylbenzo[2.2.1]cryptand wereprepared as shown in FIGS. 2 and 3. The new vinylbenzo[2.2.2]cryptand(compound 36) and vinylbenzo[2.2.1]cryptand (compound 37) polymerize byradicals in emulsions. However, any known vinyl polymerization method isalso possible including anionic, free radical and controlled freeradical polymerization methods such as RAFT, nitroxyl mediated freeradical, ATRP, and the like.

The preparation of vinylbenzo[2.2.2]cryptand andvinylbenzo[2.2.1]cryptand from 4-acetylcresol follows a similar pathwaysas that in Kopolow et al. and FIG. 3.

Compounds with hydroxyl groups are allowed to react with vinylbenzylchloride and then polymerized in emulsion, or alternatively, are allowedto react with poly(11-undecylenyl iodide) in tetrahydrofuran with sodiumhydride to prepare polymers with pendant crown ethers and cryptands.(see FIGS. 4 to 8)

Each of the vinylbenzyl compounds such as compounds 34, 35, 36, 37, and38 are polymerized in emulsion with crosslinking dimers such asdivinylbenzene or compound 30 to form nanoparticulate beads which arefurther purified by dialysis. These polymers are then added to ionomersto scavenge metal ions before the coating of electrode layers and tosequester migrating Pt(II) formed during fuel cell operation. Pt(II) isreduced back to Pt(0) by electrons at the cathode or by H₂ crossovergas.

Polystyrene crosslinked with divinylbenzene in the form of beads,fibers, particulates and nanoparticles are functionalized with metalionophores as shown in FIG. 7. These materials are used as additives infuel cell electrode layers and membrane electrode assemblies.

Polyolefins are prepared by the Ziegler-Natta polymerization of1-olefins and the polymerization proceeds with a variety of functionalgroups in FIG. 8. In this variation, undecylenyl iodide is polymerizedand then the iodo group is replaced with ionophoric groups. Thesematerials are added to ionomer coating solutions to form fuel cellmembranes.

4′-HC(O)C₆H₃(OCH₂COOH)(OCH₂COOH) (Compound 40). Under argon, ClCH₂CCOOH(23.6 g, 0.25 mol) in t-butanol (t-BuOH, 80 mL) is added slowly to arefluxing mixture of 1-HC(O)-3,4-C₆H₃(OH)₂ (3,4-dihydroxybenzaldehyde,13.8 g, 0.1 mol) and K⁺⁻OBu-t (potassium t-butoxide, 56.1 g, 0.5 mol) int-BuOH (400 mL). The mixture is refluxed and stirred for 4 h and thenstirred at 23° C. for 6 h. The t-BuOH is evaporated under vacuum, andthen H₂O (100 mL) is added. After extraction with Et₂O, the aqueouslayer is acidified with HCl and is repeatedly extracted with CH₂Cl₂. Thecombined CH₂Cl₂ solutions are centrifuged, filtered and evaporated undervacuum to yield 4′-HC(O)—C₆H₃(OCH₂COOH)(OCH₂COOH (compound 40, 10 g).

Compound 41. Compound 40 (10 g) is dissolved in 400 mL of a 1:1 volumemixture of benzene and methanol, and then p-toluenesulfonic acid (2 g)is added. The mixture is heated to reflux for 16 h with continuouscirculation of condensed vapors through anhydrous Na₂SO₄ in a thimble ofa Soxhlet extractor. The solvent is removed and an ether solution of theresidue is washed with 5% aqueous NaHCO₃. The ether layer is dried overNa₂SO₄ and then removed to yield compound 41 (10 g).

Compound 42. The diazacrown ether,1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (1 eq) in dry THF (50 mL)is treated with two equivalents of n-butyllithium (1.6 M in hexanes) andis added dropwise to compound 41 (0.5 eq) in THF (50 mL) with magneticstirring. After stirring 16 h at 23° C., the mixture is stirred atreflux for 8 h. Removal of the solvent yielded the cryptand diamide.Reduction with LiAlH₄ in THF, followed by acid hydrolysis, and thenreaction with LiCH₂P(C₆H₅)₃ in ether produces compound 42:

Compound 43. A 50 wt. % solution of aqueous sodium hydroxide (5 mL) isadded dropwise to a stirred solution of 5 g of compound 2 in methanolwhile keeping the temperature at less than 40° C. The mixture is left at23° C. for 4 h, extracted with 100 mL ether, and acidified with dilutehydrochloric acid. After repeated extraction with CH₂Cl₂, drying of thecombined organic layers over Na₂SO₄, filtration and evaporation, thediacid is obtained. The diacid (0.906 mmol) is dissolved in 20 mL of drybenzene and oxalyl chloride (10.7 g, 84 mmol) is added all at once. Asmall amount of pyridine (3 drops) is added as a catalyst which causesan immediate reaction. The flask is fitted with a drying tube andstirred for 48 h at 23° C. The mixture is then quickly filtered undernitrogen through a dry sintered glass Schlenk funnel, the solvent isevaporated in vacuo, and then co-evaporated once with dry benzene. Theresidue compound 43 is stirred under vacuum for 30 minutes and then usedimmediately after it is produced.

4′-Vinylbenzo-[2.2.2]Cryptand (compound 44). The diazacrown ether,1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, and triethylamine (2.50 g,24.7 mmol) diluted to 110 mL in toluene and the diacid chloride compound43 (9.2 mmole) diluted to 110 mL in toluene are added simultaneously to350 mL of toluene, with vigorous stirring at 0-5° C. in a Morton flaskover a period of 7-8 h. After the addition is completed, the mixture isstirred overnight at 23° C. The solid precipitate is filtered and washedwith toluene and then Et₂O. The filtrate is combined with the washingsand evaporated in vacuo, and the residue is subjected to chromatographyon alumina using EtOAc/MeOH (40:1) as eluent to give the cryptanddiamide. To a solution of the cryptand diamide (5.4 mmol) stirring at23° C. in 10 mL dry THF is added dropwise a 1.0 M solution of BH₃.Me₂Scomplex (20 mL) in THF and the mixture is stirred at reflux for 9 h. Thesolution is cooled to 23° C., then cooled in an ice bath, and water (5mL) is added slowly to destroy the excess BH₃. The solution isevaporated in vacuo and the remaining solid is refluxed in a mixture ofwater (10 mL) and 6 N HCl (15 min) for 12 h. After cooling the solutionto 23° C., 50 wt. % NaOH is added slowly with stirring to adjust the pHto 10 and the solution is evaporated in vacuo. The resulting precipitateis washed with 2×30 mL of MeOH. The washings are combined afterfiltration and Et₂O is added to precipitate the inorganic salts byadding a small amount of Et₂O, filtering the solution, collecting thefiltrate and then adding more Et₂O. This is done repeatedly, evaporatingsome solution to reduce the volume needed, until no more solidprecipitated from solution. The filtrate is evaporated in vacuo and theresidue is purified by chromatography on alumina using CHCl₃/MeOH (25:1)as eluent to give 4′-formylbenzo-[2.2.2]cryptand. Alternatively, thecyclic diamide in THF (20 mL) is added at 23° C. to a stirred suspensionof LiAlH₄ in THF (20 mL). The solution is stirred at reflux for 24 h,cooled to 23° C. and then to 0° C. with an ice bath. A solution of 15%NaOH (2 mL) is added and the suspension is stirred 24 h. Afterfiltration and solvent evaporation, the residue is subjected tochromatography on alumina using CHCl₃ and ethanol (25:1) as eluent togive the cryptand. Using a gas-tight syringe, 1.2 mL of a 1.6 M solutionof n-butyllithim in hexanes is added to methyltriphenylphosphoniumbromide (2.11 g) in dry ether (100 mL) under argon with magneticstirring. The yellow mixture is boiled at reflux under argon for 1 hour,and 4′-formylbenzo-[2.2.2]cryptand (1.2 g) in dry ether (50 mL) is addeddropwise. Boiling at reflux is continued for 1 h and then the reactionis stirred 48 h at 23° C. The solution is filtered and the ether layeris filtered through a plug of Merck silica in a column eluting withether. After a second filtration through a plug of silica with ether,the ether is removed and 4′-vinylbenzo-[2.2.2]cryptand, (1 g) isobtained.

Preparation of [4′-HC(O)C₄H₃(O—)₂(CH₂CH₂OCH₂CH₂OCH₂CH₂)] (compound 45)and Compound 46. To 1-L of t-butanol is added 1-HC(O)C₄H₃(OH)₂(3,4-dihydroxybenzaldehyde, 0.2 mol, 27.6 g) and the mixture is purged0.5 h under N₂. A solution of K⁺⁻OBu-t (46 g, 0.41 mol) is added int-BuOH (328 mL), and then (ClCH₂CH₂OCH₂CH₂)₂0 (46.2 g, 0.2 mol) is addedover 15 minutes. The reaction mixture is then refluxed 24 hours. Themixture is cooled, and the solvent is removed using a rotary evaporator.Water is added and the mixture is extracted multiple times with CH₂Cl₂,the combined organic layers are dried over sodium sulfate, filtered andthen the solvent is evaporated. The residue is extracted multiple timeswith ether (0.5 L each) to yield 20 g of[4′-HC(O)C₄H₃(O)₂(CH₂CH₂OCH₂CH₂OCH₂CH₂)], 4′-formylbenzo-15-crown-5(compound 45), and compound 46.

Preparation of [4′-HC(O)C₄H₃(O—)₂(CH₂CH₂OCH₂CH₂OCH₂CH₂)] (compound 45)and Compound 46. To 1-L of t-butanol is added HC(O)C₄H₃(OH)₂(3,4-dihydroxybenzaldehyde, 0.2 mol, 27.6 g) and the mixture is purged0.5 h under N₂. A solution of K⁺⁻OBu-t (46 g, 0.41 mol) is added int-BuOH (328 mL), and then (ClCH₂CH₂OCH₂CH₂)₂O (46.2 g, 0.2 mol) is addedover 15 minutes. The reaction mixture is then refluxed 60 hours at 70°C. The mixture is cooled, and the solvent is removed using a rotaryevaporator. The residue is washed with hexanes to remove residualunreacted ether and then is washed with diethyl ether. Aqueous 10 wt. %hydrochloric acid (100 mL) is added and the mixture is extractedmultiple times with CH₂Cl₂. The combined organic layers are separatedwith the aid of a centrifuge and then dried over sodium sulfate,filtered and then the solvent is evaporated. The residue is extractedmultiple times with ether (0.5 to 1 g of 4 dissolves in 1 L of ether) toyield 9.66 g of recrystallized [4′-HC(O)C₄H₃(O)₂(CH₂CH₂OCH₂CH₂OCH₂CH₂)],4′-formylbenzo-15-crown-5 (compound 45), and compound 46 (1.256 g).

Preparation of6,7,9,10,12,13,15,16,23,24,26,27,29,30,32,33-hexadecahydrodibenzo[b,q][1,4,7,10,13,16,19,22,25,28]decaoxacyclotriacontine-2,20-dicarbaldehyde(compound 47). The methyl Grignard is made by adding MeI (17.5 g) anddry ether (50 mL) to 3 g Mg in dry ether (20 mL). After the Mgdissolves, 7 g of compound 46 in 400 mL of dry ether/100 mL of drybenzene are added dropwise. A white precipitate forms immediately. Aftercomplete addition, the mixture is heated 1 h at reflux, then cooled, and15% aq NH₄Cl solution is added until two layers form. The aqueous layeris extracted 4 times with 100 mL CHCl₃. The Et₂O and CHCl₃ layers arecombined and dried. The residue is recrystallized from 500 mL ether togive 5 g of compound 47:

2,20-divinyl-6,7,9,10,12,13,15,16,23,24,26,27,29,30,32,33-hexadecahydrodibenzo[b,q][1,4,7,10,13,16,19,22,25,28]decaoxacyclotriacontine(compound 48). A trace of p-toluenesulfonic acid monohydrate is added to4 g compound 47 in 350 mL benzene. The mixture is refluxed with removalof H₂O for 14 h. After cooling to 23° C., 5 drops of pyridine are added.Benzene is evaporated and the product crystallizes on standing. Compound48 is dissolved in 100-mL CH₂Cl₂, extracted 4 times with 100-mL H₂O, andthen the CH₂Cl₂ is dried over Na₂SO₄. The CH₂Cl₂ is removed, and theresidue recrystallizes from petroleum ether (1 g of compound 48 in 75mL) to give 3 g of compound 48:

Preparation of 11-Undecylenyl iodide. To a 250-mL round-bottom flaskwith mechanical stirrer, reflux condenser and addition funnel are addedNaI (43.5 g, 0.29 mol) and acetone (75 mL). Undecylenyl chloride (43 g,0.2226 mol) is added dropwise and the mixture is refluxed for 16 h. MoreNaI (9 g) is then added and boiling at reflux is continued for 4 days.CH₂Cl₂ is added, and the reaction mixture is filtered. The solvent isremoved and the residue is vacuum distilled. The fraction collectedbetween 95-98° C. at 1 mm Hg is 11-iodoundecene.

Preparation of Poly(11-undecylenyl iodide). Undecylenyl iodide (5 g),toluene (30 g), Et₂AlCl (10 mL of a 1.8 M solution), TiCl₃.AA (0.5teaspoon, ≈2 g), and 16 h at 25° C. are combined. After 16 h, themixture is blended with methanol, and the filtered polymer is washedwith water and then methanol. Other ratios used include: undecylenyliodide (12 g), toluene (40 g), Et₂AlCl (22 mL of a 1.8 M solution),TiCl₃.AA (1 teaspoon), and then 16 h at 25° C.

Reaction of Cryptand (compound 49) and Poly(11-undeclenyl iodide).Freshly distilled tetrahydrofuran (100 mL) and about 60 wt. % sodiumhydride in mineral oil (6 g) are added to poly(11-undecylenyl iodide) (1g). With magnetic stirring under argon, compound 49 (2 g) is added andthe mixture is stirred at 23° C. for 7 days. Isopropanol is addedcautiously to quench the remaining sodium hydride. The reaction mixtureis concentrated using a rotary evaporator and then is added to water(100 mL). The mixture is centrifuged and the solids are washed withwater, centrifuged, and then dried.

Reaction of 2-Hydroxymethyl-18-crown-6 and Poly(11-undecylenyl iodide).Freshly distilled tetrahydrofuran (100 mL) and about 60 wt. % sodiumhydride in mineral oil (6 g) is added to poly(11-undecylenyl iodide) (1g). With magnetic stirring under argon, 2-hydroxymethyl-18-crown-6(compound 31, 2 g) is added and the mixture is stirred at 23° C. for 7days. Isopropanol is added cautiously to quench the remaining sodiumhydride. The reaction mixture is concentrated using a rotary evaporatorand then is added to water (100 mL). The mixture is centrifuged and thesolids are washed with water, centrifuged, and then dried. Increasingthe reaction temperature turns the resultant polymer brown withoutfurther increasing the replacement of iodide by the2-hydorxymethyl-18-crown-6, as determined with infrared spectroscopy.

Polymerization of 4′-Vinylbenzo-18-Crown-6. Compound 35[4′-vinylbenzo-18-crown-6 (3 g)] and divinylbenzene (0.1 g) are added toa mixture of potassium persulfate (0.02 g), sodium hydrogen phosphate(0.02 g) and sodium dodecylsulfate (0.2 g) in 40 mL of deionized waterin a beverage bottle (6.5 fluid ounce volume) equipped with a rubberseptum and a magnetic stir bar. The emulsion is sparged with argon for30 minutes and is then heated at 70° C. for 48 hours. After cooling, thecontents of the bottle are transferred to Spectropore dialysis tubingand dialyzed for 1 week against 4-liters of deionized water with waterchanges occurring at least twice per day. The residue is freeze dried toyield 3 gram of fibers.

Emulsion Polymerization of 4′-Vinyl benzo-18-crown-6. To a 50-mL,one-neck flask with a 14/20 joint is added a stir bar, water (10 g),potassium persulfate (0.005 g), sodium hydrogen phosphate (0.005 g), andsodium dodecyl sulfate (0.05 g). After this mixture dissolves,4′-vinylbenzo-18-crown-6 (Sigma-Aldrich, 1 g) and freshly distilleddivinylbenzene (1 drop, 0.05 g) is added. The flask is then equippedwith a reflux condenser, a yellow Keck clamp, and a rubber suba sealseptum for sparging the liquid with argon using a long needle for anargon gas inlet and another needle connected to a silicone oil bubblerfor an exit. Argon is passed over the emulsion to replace the air anddisperse the reactants for 30 minutes. The argon is removed and themixture in the sealed flask is stirred in a 70° C. oil bath for 2 h,then at 95° C. (oil bath set temperature) for 16 h. The cooled emulsionis transferred to a dialysis tube (Spectropore) and dialyzed for 1 weekwith frequent water changes. After freeze-drying 0.9 g ofpoly(vinylbenzo-18-crown-6) is obtained in the form of 120 nm diameterwhite beads. These beads are added to ionomer solutions such as TCT891(Tetramer Technologies, L.L.C.), NAFION® DE2020® (DuPont deNemours),IG100 (Asahi Glass), and the like, and are used in fuel cell electrodelayers. One fuel cell test is performed with the beads remainingsuspended in the ionomer solution before coating at 5 wt. %poly(vinylbenzo-18-crown-6) based on ionomer solids. Another fuel celltest is performed after centrifuging the ionomer mixture and decantingthe ionomer solution from the sediment at the bottom of the centrifugevessel. The liquid ionomer phase is then about 100 nm in diameter.TCT891 is a perfluorocyclobutane multi-block co-polymer withperflurosulfonic acid side groups available from Tetramer Technologies,LLC. The structure is shown below. The molar ratio of biphenyl tohexafluoroisopropylidene biphenyl moieties is 2 to 1, and the ionexchange capacity of the polymer is 1.55 meq H⁺/g ionomer. The overallnumber average molecular weight of the polymer by size exclusionchromatography is 60,000, while that of the biphenyl chains is about8,000. The hexafluoroisopropylidene biphenyl groups are interspersedbetween the 8000-number average molecular weight biphenyl segments(about 9 groups) in a less defined way, because these are introducedindividually during the polymerization instead of being added as anoligomer segment. The polydispersity of the polymer, defined as weightaverage molecular weight divided by number average molecular weight, is1.3. The polymer is soluble in alcohols (methanol, ethanol, 1-propanoland isopropanol) and in polar aprotic solvents such asN,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

Polymers with this structure are further described in U.S. Pat. Nos.7,897,691; 7,960,046; and 8,053,530.

In general, the polymers which include cyclic polyether groups are usedin an anode ink and in particular, a cathode ink, as an additive to formfuel cell anodes and cathodes.

MEA Preparation Using Poly(vinylbenzo 18-crown-6) as Cathode Additive

The synthesized poly(vinylbenzo-18-crown-6) is incorporated as anadditive to the cathode ink solution at 5 wt. % based on ionomer weightto fabricate cathode electrodes with a target loading of ˜0.2 mg Pt/cm².Membrane-electrode-assemblies (MEAs) are made with the prepared cathodealong with the standard anode with a loading of 0.05 mg Pt/cm². The MEAsare tested for fuel cell performance (i.e., polarization curves) usingH₂/air (anode/cathode), cathode oxygen reduction reaction (ORR) kineticactivities using H₂/O₂ (anode/cathode), and durability byvoltage-current cycling (V-C cycling) at 80° C. Results are comparedwith MEAs made with standard cathode and anode.

Electrode Ink Preparation. The cathode ink solution is prepared on a 40g scale and the ingredients used in the formulation are listed in Table1 as below. The mixture solution is ball-milled with ZrO₂ beads for 3days before coating. Standard anode with 0.05 mg Pt/cm² is prepared from20% Pt/V (graphite) and IG100 ionomer (Asahi Glass). The weight ratio ofionomer to carbon (I/C ratio) is fixed at 0.95 for the cathode and 0.6for the anode to ensure good coating quality.

TABLE 1 The cathode ink formulation with 5 wt. % additive ofpoly(vinylbenzo- 18-crown-6) based on ionomer at a loading of 0.2 mgPt/cm². Ingredients Mass (g) 30% PtCo/HSC Alloy Catalyst 1.74 ZrO₂ Beads(5 mm) 50.00 H₂O 4.99 EtOH 29.29 IG100 (28.62 wt % in EtOH:H₂O = 3.9860.1:39.9) Poly(vinylbenzo-18-crown-6) 0.06 Ink Total 40.06

TABLE 2 The standard cathode ink formulation at a loading of 0.2 mgPt/cm². Ingredients Mass (g) 30% PtCo/HSC Alloy Catalyst 1.74 ZrO₂ Beads(5 mm) 50.00 H₂O 4.99 EtOH 29.29 IG100 (28.62 wt % in EtOH:H₂O = 3.9860.1:39.9) Ink Total 40.00

MEA Preparation. Electrode inks are coated using a Meyer rod onpoly(ethylene-tetrafluoroethylene) (ETFE) substrate and then decaltransferred. The die-cut cathode- and anode-coated decals with an activearea of 50 cm² were hot pressed onto the NAFION® 211 (25 μm, 1100 EW)membrane at 295° F. for 2 min at 0 lbs and 2 min at 5000 lbs. The 50-cm²catalyst coated membrane (CCM) is built with carbon paper coated with aproprietary microporous layer that serves as gas diffusion media (GDM),and with “dog-bone” flow-fields for small-scale (50-cm² active area)single-cell tests.

H₂/Air Fuel Cell Performance Test. Fuel cell performance (FCPM) istested with stoichiometries of 1.5 to 2.0 for H₂ and air at anode andcathode, respectively, (1.5/2.0 stoic, A/C) and 32% and 100% inletrelative humidity (RH_(in)). The current density is controlledsequentially at 0.05, 0.2, 0.4, 0.8, 1.0, 1.2, and 1.5 A·cm⁻².Polarization curves are plotted in the format of cell voltage versuscurrent density under 32% and 100% RH_(in), which is denoted as FCPM andWet-FCPM, respectively.

Cathode ORR Kinetic Activity Test. The cathode oxidation-reductionreaction (ORR) is tested under 100% RH_(in) and 2.0/9.5 stoichiometriesfor H₂ and O₂ (A/C). The cell total pressure is maintained at 150kPa_(abs). The current density is controlled sequentially at 0.02, 0.03,0.05, 0.1, 0.2, and 0.4 A·cm⁻². The catalytic activity of the cathodecatalysts is evaluated at a high frequency resistance (HFR)-correctedvoltage of 0.9 V vs. reference hydrogen electrode (RHE) at 80° C.

Voltage Cycling Test. H₂ (200 standard cm³, sccm) and N₂ (50 sccm) arefed into the anode and cathode at 150 kPa_(abs) in the voltage cyclingtest. The cell voltage is swept at 50 mV·s⁻¹ between 0.6 and 1.0V_((RHE)) in a triangle profile for up to 30,000 cycles.

Results and Discussion. The MEAs are subjected to the cathode catalyticactivity (H₂/O₂) and the H₂/air performance tests before voltage cyclingdesignated the beginning of life, (BOL, 0 cycles), and then after 10,000voltage cycles and then after 30,000 voltage cycles, designated the endof life (EOL) of voltage cycling. The test results are shown graphicallyin FIGS. 9-16. Mass activity and the cell voltage at the current densityof 1.5 A/cm² are summarized in Table 3. As shown, the sample MEA madewith 5 wt. % poly(vinylbenzo-18-crown-6) in the cathode has a highermass activity and fuel cell performance voltage than those of thebaseline MEA (without polymeric crown additive) during all of the teststages. Analyses are performed on the baseline MEA sample and the MEAsample with 5 wt. % poly(vinylbenzo-18-crown-6) in the cathode at thebeginning of life and after 30,000 C-V cycles. Cross-section images areall aligned with the anode side up. FIG. 9(B) shows that the baselineMEA has a bright Pt-line at the membrane-cathode interface after beingtested for 30,000 CV cycles; whereas, there is a much-less obviousPt-line in the MEA with the poly(vinylbenzo-18-crown-6) additive in thecathode [FIG. 10(B)]. Two proposed mechanisms of catalyst activity lossare (1) the Oswald ripening of the Pt catalyst particles (dissolutionand re-deposition of smaller particles to form bigger particles) and (2)Pt dissolution and diffusion towards the membrane. Although the amountof required poly(vinylbenzo-18-crown-6) additive has not been optimized,5 wt. % of this additive to the cathode electrode reduces Pt dissolutionand diffusion as evidenced by a distinct Pt line at theelectrode-membrane interface [compare the white Pt line of FIG. 9(B) andthe absence of this line in FIG. 10(B)]. The voltage-cycled electrodewith the polymeric crown ether additive pictured in FIG. 10(B) has Ptdistributed uniformly throughout the electrode layer as white speckles.

TABLE 3 Summary of testing results. Actual Pt Mass FCPM Wet-FCPM loadingActivity Voltage at Voltage at Sample Description mg/cm² (A/mg) 1.5A/cm² 1.5 A/cm² NRE 211 with Cathode 0.1709 0.488 0.547 0.621 Additive(BOL) NRE 211 with Cathode 0.1709 0.428 0.483 0.557 Additive after 10kcycles NRE 211 with Cathode 0.1709 0.298 0.371 0.439 Additive (EOL) NRE211 Baseline 0.1735 0.334 0.521 0.601 (BOL) NRE 211 Baseline after0.1735 0.263 0.471 0.57 10k cycles NRE 211 Baseline (EOL) 0.1735 0.2060.412 0.516

FIG. 9 provides cross-section images of baseline MEA at BOL (A) andafter 30,000 C-V cycles (B). FIG. 10 provides cross-section images ofMEA with 5 wt. % poly(vinylbenzo-18-crown-6) additive in the cathode atBOL (A) and after 30,000 C-V cycles (B). FIG. 11 provides small-scale(50-cm² active area) fuel cell performance of a sample with 5 wt.%poly(vinylbenzo-18-crown-6) additive in the cathode (BOL) (A) andcatalyst mass activity plot (BOL) (B). FIG. 12 provides small-scale fuelcell performance of sample with 5 wt.% poly(vinylbenzo-18-crown-6)additive in the cathode after 10,000 voltage cycles (A) and catalystmass activity plot (B). FIG. 13 provides small-scale fuel cellperformance of sample with 5 wt.% poly(vinylbenzo-18-crown-6) additivein the cathode after 30,000 voltage cycles (A) and catalyst massactivity plot (B). FIG. 14 provides small-scale fuel cell performance ofsample baseline (BOL) (A) and catalyst mass activity plot (B). FIG. 15provides small-scale fuel cell performance of sample baseline after10,000 voltage cycles (A) and catalyst mass activity plot (B). FIG. 16provides small-scale fuel cell performance of the baseline sample after30,000 voltage cycles (A) and catalyst mass activity (MA) plot (B).

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

1-11. (canceled)
 12. An ink composition for forming fuel cell catalystlayers, the ink composition comprising: a first polymer including cyclicpolyether groups; a catalyst composition; and a solvent system.
 13. Theink composition of claim 12 wherein the catalyst composition is presentin an amount of about 1 weight percent to 10 weight percent of the totalweight of the catalyst composition, the catalyst composition includes asupported catalyst dispersed within an ionomer solution.
 14. The inkcomposition of claim 12 wherein the supported catalyst is present in anamount from about 5 weight percent to about 40 weight percent of thecatalyst composition.
 15. The ink composition of claim 12 wherein thesolvent system is present in an amount from about 20 to 80 weightpercent of the total weight of the ink composition.
 16. The inkcomposition of claim 12 wherein the first polymer including cyclicpolyether groups is a linear oligomer.
 17. The ink composition of claim16 wherein the linear polymer has the following formula:

where R₁ is absent or a hydrocarbon group and CPG is a cyclic polyethergroup.
 18. The ink composition of claim 17 wherein R₁ is C₁₋₂₀ alkyl,C₁₋₁₈polyether, C₆₋₂₀ alkylaryl, or C₆₋₂₀ aryl.
 19. The ink compositionof claim 18 wherein CPG is selected from the group consisting of:


20. The ink composition of claim 12 wherein the first polymer includingcyclic polyether groups is a cyclic oligomer.
 21. The ink composition ofclaim 12 further comprising a second polymer having sulfonic acid groupsselected from the group consisting of perfluorosulfonic acid (PFSA)polymers, polymers having perfluorocyclobutyl moieties, and combinationsthereof.